Ihsulated fusible plug for steam-boilers



l UMTED STATES PATENT orrroE.

l lE. H. ASHCROF'I,` 0F BOSTON, h'IASSACI-IUSETTS.

. INSULATED FUSIBLE PLUG FOR STAlVI-BOILERS.

Speeifeatien of Letters Patent No.`

To all whom t concern i Be it knownthat I, E. H. ASHCROFT, of Boston, in the county of Suffolk and State of Massachusetts,` have invented a new and useful Method of Applying Fusible Safety Plugs to Steam-Boilers; and Ido hereby declare that the following is a full, clear, and exact description thereof, reference being had to the accompanying drawings, which form part of this specification, and in whichi Figures l, 2, `3, and 4 represent two varieties of my insulated fusible plug in perspective and in section, and Figsf, 6,\and 7, represent sections of boilers with insulated plugs applied thereto. c

The first part of my invention consists in inserting the fusible plug ina case in such a manner that both plug and case are protruded into the fire chamber or flues of a boiler in suchmanner that both plug and case are insulated from the water immediately in contact with the boiler plates by a stratum of air; the latter prevents the transmission of heat from `the plug-case to a stratum of water of merely suiflcientdepth to cover the plates of the boiler to which the plug `case is al'liXed, but does not prevent its transmission to the water above, hence as long as the boiler is properly supplied with water the plugwill remain unfused, for the heat imparted `to it by the flame will be transmitted to the water; but whenever the `water evaporates down to a predetermined limit the plug, being insulated by the air from the water still covering the boiler plates will melt and, allowing the steam to escape, will give warning of the deficiency of water and approach of danger before the plates have becomebare, and consequently beforethe danger of an explosion has become imminent.

The second part of my invention relates to the construction and arrangement of a fusible plug lwhich is such that when one of my plugs has melted and allowed steam to escape from the boiler and give warning of a deficiency of water, t-he escape of steam `can be stopped and a new fplug can be inserted without blowing o water in the boiler.

In the accompanying drawing, a a is the plate of the fire or flue surface of a boiler to which my safety apparatus is applied. In the variety represented at Figs. l and 2 the plug case A is screwed into the tubular the steam or 7,934, dated February is,` 1851.

`shank of'a hollow block C. The latter is perforated to admit a tube D which is screwed at its lower extremityunto the block C while its opposite extremity is passed through the exterior shell cl of the boiler and is open to the air. rIhe lower extremity of the tube D is closed by screwing it down `firmly upon the head of the fusible plug c in the plug case, and that part of the tube which passes through the shell ofthe boiler is secured by double nuts g, g, or `in any other convenient manner which will hold it firmly and prevent the leakage of steam. The block C is secured to the upper part of an air chamber whose lower extremity is passed through and secured to the bo-iler plate a.. The hollow space 7L in the block C is connected by a small tube I with that portion of the boiler occupied by the steam, the upper end of this tube is open so that steam can pass freely through it into the hollow space 7a A screw stopper 7c is inserted ,thro-ugh the shell of the boiler imme-,

diately opposite the open end of this tube, its outer extremity being formed into a head to which a wrench can be applied to screw the stopper downward until its inner extremity, which is conical, enters the open extremity of the steam tube I and closes it.

The plug case A,hollow block C, and air chamber E should be made of some material (copper for example) which is afgood conductor of heat andthe plug e should be made as usual of either lead or tin, or of some alloy still more fusible, `as for example an alloy of lead and bismuth, according to the temperature at which it is desired it should melt.

It will be perceived from the foregoing description and the accompanying drawing that the stratum of air m by which the plug case is surrounded prevents the direct transmission of heat from it toany ,water which may surround the air wchamber, while the block C will transmit the heat from the plug case to any water which may `be above the air chamber; consequently as long as there is a suflicient quantity of water in the boiler to cover the block C the temperature of the plug case will be kept below` the fusing point of the plug, but if the water in the boiler be evaporated down slightly below the level of the upper surface of the stratum of air surrounding the plug case, the latter being insulated by the air, (which is an eX- tremely bad conductor `of heat), from the water still remaining in the boiler, will no longer have the heat conveyed from it as fast as it is imparted to it by the fire;- the plug will consequently melt and will run down to the lower part of the plug case, leaving the lower extremity of the t-ube D, unclosed to permit the steam passing down the steam tube I to escapeland give warning of the low state of the water. As this warning is given while the boiler plates are still covered with a stratum of water extending nearly to the top of the air chamber they are still in their usual comparatively cool state, and consequently the warning is given before the boiler has arrived at a dangerous condition by the undue heating of the boiler plates which takes place when Vthey are no longer covered by water.

IVhen the warning has been given the first duty of the engineer is to see that the feed pumps supply a sufficient quantity of water to make good the deficiency, he may then screw down the stopper 712 and close the steam tube, by which means the further escape of steam is stopped.v The fire should then be dampened sufliciently to enable the engineer to insert proper' tools through the lire door of the boiler to unscrew the plug case and to replace it with another having a new plug in it. The stopper 7c can then be screwed up to open the steam tube I and the apparatus will be ready to indicate any renewed deficiency in the supply of water.

In order to prevent the loss of the fusedl metal of the plug and the escape of steam into the fire chamber the lowerwextremity of the socket of the plug case is closed by a screw stopper 0.x;

The apparatus represented at Figs. 3 and 4 is simpler in its construction than that above described. In this' example the tubes are dispensed with and a screw stopper 7c is inserted through the shell of the boiler immediately opposite the inner extremity of the fusible plug e. The lower extremity of this stopper is of such shape that when the plug melts lit can be screwed downward upon the orifice of the socket in the plug case to close it. The lower extremity of the socket is open so that when the plug melts through a deficiency of Water the steam blows it downward and escaping into the lire-chamber gives warning of the low state of the water at the same time acting to dampen the fire. The stopper may then be screwed down to arrest the escape of steam and, water being supplied, the` boiler is again in working order. If it be deemed advisable a new plug case may be inserted in the same manner as above described.

I have found it most convenient to form the air space m by securing a separate chamber E to the boiler' plates, but it may in some instances be expedient to form the air chamber out of the boiler plate itself by bulging it up at this point to the requisite height.

That I clailn as my invention and desire to secure by Letters Patent isl. The arrangement herein described for surrounding a fusible plug and its `case by a stratum of air in such manner that the plug shall promptly melt and give Warning after the water gets low in the boiler but before the boiler plate to which the apparatus is applied is left bare of water substantially as herein set forth.

2. I also claim the arrangement of the stopper and plug case substantially as herein described for stopping the escape of steam to admit of the replacement. of the fusible plug without blowing off the Steam or water from the boiler after the plug has melted substantially as herein set forth.

I likewise claim the method of preventing the waste of the metal of the plug after it has melted by supporting it in a closed socket the lower unoccupied part of whichl is of suficient capacity to receive andretain the metal when melted and to allow the steam to pass over it to escape.

In testimony whereof I have hereunto subscribed my name.

, E. H. ASHCROFT.

litnesses z I. A. ANDREW, GEO. W. CoLLAMoRE. 

